The Environmental Protection Agency (EPA) has set diesel engine emission requirements including NOx and non-methane hydrocarbons below 0.20 grams bhp-hr and 0.14 grams/bhp-hr, respectively. This contrasts with current standards of 4.0 grams/bhp-hr and 1.3 grams/bhp-hr, respectively. Thus, the diesel engine emission control systems must accomplish a significant reduction in NOx and PM.
Apparatus that oxidizes engine fuel to provide a mix that enhances NOx reduction is disclosed in U.S. Pat. No. 5,412,946, in PCT published application WO 01/34950, and U.S. patent application Publication 2001/41153.
In commonly owned U.S. patent application Ser. No. 10/159,369, filed May 31, 2002, moisture and possibly oxygen, derived from the exhaust of a hydrocarbon-fueled, internal combustion engine are processed along with fuel from the engine's fuel tank in a fuel processor, which may be a catalytic partial oxidation reformer, a homogeneous non-catalytic partial oxidation reformer, or an auto thermal reformer, to generate a stream including hydrogen and carbon monoxide (syngas) which is used to regenerate NOx traps following the formation of nitrogen-containing compounds by reaction of the exhaust with adsorbent in the NOx traps.
In FIG. 1, an engine 9 has a conventional turbo compressor 10 feeding an air inlet line 11, a hydrocarbon fuel tank 12, and a fuel pump 13. The fuel may be diesel fuel, gasoline, natural gas, liquid petroleum gas, or propane. The fuel is fed by a first line 17 to the engine for combustion with the air, and is fed by a second line 18 through a heat exchanger 50, to a mixer 19 in a pipe 20 that feeds a small amount of exhaust from an exhaust pipe 21 to a syngas generator 22. The heat exchanger 50 causes heat of the engine exhaust to preheat or vaporize the fuel in the line 18 before applying it to the syngas generator.
The syngas generator 22 may be a catalytic partial oxidizer (CPO), a homogeneous non-catalytic partial oxidizer (POX), or an auto thermal reformer (ATR). Within a CPO, foam monolith or other form of catalyst, which may comprise a group VII metal, preferably nickel, cobalt, rhodium, iridium, palladium or platinum, converts fuel along with water and oxygen into a mix of hydrogen, CO and CO2, which is commonly called “syngas”. This is provided through a conduit 26 to a continuously operable regenerating NOx adsorption bed apparatus 52, in which the filter itself may rotate with a stationary inlet manifold, or the inlet manifold may rotate with a stationary filter, as described more fully in U.S. patent application Ser. No. 10/309,712, filed Dec. 4, 2002 and in FIGS. 2-6 herein.
Although various adsorbents may be used, the NOx traps may, for example, contain barium carbonate (BaCO3) as the adsorbent. Typically, a catalyst, such as platinum, may be dispersed on the adsorbent material to catalyze the NOx reduction reaction. When the diesel exhaust is adsorbed by the barium carbonate, a reaction, catalyzed by platinum, generates barium nitrate.2NOx+BaCO3→Ba(NO3)2+CO2 
Then, during the regeneration cycle, the barium nitrate is converted catalytically in the presence of a noble metal catalyst, such as platinum, back to barium carbonate, as follows:3H2+2CO+Ba(NO3)2→BaCO3+N2+3H2O+CO2 
A CPO reformer is preferred in one sense because it is very small and can run with low steam carbon ratios and high turndown ratios without soot or carbon formation. However, diesel engine exhaust contains particulates (soot) and oxides of sulfur (SOx), which may deactivate the CPO catalyst over a period of time. Therefore, a homogeneous non-catalytic partial oxidizer (POX) may alternatively be selected as the syngas generator 22. The percentage of hydrogen produced is only slightly less than that produced by a CPO. It is easily started by employing a simple spark plug, as is known. Additionally, POX is cheaper than CPO; control of the O2/C ratio is known (similar to engine O2/fuel ratio), and simpler; SOx and soot do not affect it; and the challenges of steam/C and O2/C ratio control problems are much easier to handle compared with that of a CPO.
Because the alternating absorption and regeneration cycles have difficulty with high temperature valves, which allow on the order of 5% of total engine exhaust to leak through the wrong absorption bed during regeneration, thereby wasting a significant amount of syngas by combusting with the oxygen in the exhaust, the invention in the parent application provided a relatively rotating inlet gas distributor and NOx adsorption bed having a plurality of flow paths lined with adsorption catalyst. The exhaust flows in a given path during a first fraction of a revolution, during which time the NOx is adsorbed therein, and syngas flows into each path during the remainder of each revolution. Both exhaust gas and syngas are flowed continuously through the NOx adsorption bed.
Using the improved NOx adsorption bed of the parent application still requires that there be a particulate filter to reduce particulate emissions, and some accommodation to handle sulfur, which is adsorbed onto the NOx adsorbent and reduces its effectiveness. The processes are:    SOx trap: BaCO3+SOx→BaSO4+CO2     SOx regen (at high temp): BaSO4→BaO+SOx or    SOx regen (at high temp): BaSO4+CO2 BaCO3+SOx
In a particulate filter, extra fuel or syngas must be burned to raise the temperature of the particulate filter in order to initiate the particulate oxidation process once in a while (when enough particulates accumulate on the filter). Extra controls are required for periodical regeneration of the particulate filter. As a result of diesel engine exhaust, the NOx adsorber catalysts, which contain platinum over barium oxides, could be deactivated due to sulfur, phosphate, zinc or other components in the diesel fuel or in the lubricants of the diesel engines. Thus, regenerating the NOx adsorber catalyst from the effects of those contaminants must be accommodated.